The three steps through which external stimuli such as acetylcholine trigger the release of enzymes from the pancreas will be studied in isolated pancreatic acini. First, receptors for acetylcholine (ACh) will be characterized by the use of tritiated quinuclidinyl benzilate as a radioactive ligand. Receptors occupancy will then be correlated to both the secretion of amylase and the activation of nonsecretory functions such as glucose uptake, uridine transport, and protein synthesis. Second, the mechanism by which ACh and hormones such as cholecystokinin (CCK) mobilize intracellular Ca2 ion will be studied. The role of the endoplasmic reticulum (ER) mitochondria and the plasma membrane in cellular Ca2 ion regulation will be examined. The previously described microsomal Ca2 ion sequestering system will be further purified. The mechanism by which receptor occupancy leads to changes in Ca2 ion transport by isolated ER, including the role of phosphorylation of protein components of the ER membrane, will be studied. Third, to identify the mechanism by which Ca2 ion activates secretion we will investigate both the role of calmodulin (or a related protein) as a calcium receptor and whether the effects of secretagogues such as ACh are mediated by activation of specific kinase that lead to the phosphorylation of specific proteins on granules of plasma membranes. In addition acini will also be incubated with 32P to label endogenous ATP and phosphorylated proteins will be evaluated by gel electrophoresis.